1. Field of the Invention
The present invention relates to an inkjet printing apparatus that controls drive of nozzles, and a method for controlling drive of nozzles in the inkjet printing apparatus.
2. Description of the Related Art
A printhead of an inkjet printing apparatus includes multiple nozzles (discharge orifices) for discharging ink, each nozzle including an discharge pressure generating element. High-density arrangement of multiple nozzles achieves high image quality and high speed printing. Normally, not all of the nozzles of the inkjet printhead discharge ink droplets at once, and printing is performed while shifting the timing of discharge of ink droplets for each predetermined number of nozzles.
One example of a method for shifting the timing of discharge for each predetermined number of nozzles is that nozzles are divided into sections (groups), each including a predetermined number of nozzles, in accordance with their physical positions in a nozzle array of the inkjet printhead, and in each divided section, drive timings of the discharge pressure generating elements of nozzles are shifted. In order to drive all of the nozzles in each section at different drive timings within a predetermined period of time, each section is divided into multiple drive blocks, and the discharge pressure generating elements per drive block are driven at different times (time-division driving). Note that, in time-division driving performed per drive block, the same drive blocks from each section are driven at the same time, so ink is discharged from one nozzle from each section at once. Such a printhead driving method is referred to as a “separation and division drive system”. This separation and division drive system is effective to make compact a power supply for drive of an inkjet printhead, or a power supply member such as a connector or a cable.
In performing printing with such a printhead, the sequence in which blocks are driven has a great influence on the image quality of a printed image. Shifts in drive timings of nozzles to be used appear as shifts in landing positions of ink dots formed on a paper surface. Therefore, clearances are generated, in places of a print area, between ink dots (printed dots) formed on the paper surface, and accordingly a difference arises in the ink coating condition. Such a difference in the ink coating condition leads to degradation of image quality such as uneven density or the presence of streaks.
In view of such problems, Japanese Patent Laid-Open No. 7-60968 discloses a method in which, when an image is printed in multi-pass printing using multiple ink discharge nozzles, the sequence in which the discharge nozzles are driven is varied for each print pass. According to the description of this method, by varying the sequence in which the printhead nozzles are driven depending on the landing diameter or the dot density, it becomes possible to optimize dot placement on a paper surface and to thereby improve the ink coating condition on the paper surface (increase the area factor). In particular, it is possible with this method to obtain high-density and high-image-quality print results on such a print medium as plain paper that greatly suffers from ink spreading.
According to the method described in Japanese Patent Application Laid-Open No. 7-60968, it is actually possible to improve the ink coating condition on such a print medium as plain paper that greatly suffers from ink spreading. However, in the case where output results with high image quality are required with glossy paper or coated paper, it is not possible to achieve sufficient image quality even in multi-pass printing performed by simply changing the sequence in which discharge nozzles are driven, for each print pass. It has also been known that, even if the sequence in which nozzles are driven is varied for each print pass, image quality might deteriorate, depending on the set sequence in which nozzles are driven, due to occurrence of horizontal streaks or uneven density in the horizontal direction. Hence, technology for setting a sequence in which nozzles are driven for each print pass is important because image quality is greatly affected by superfine differences in landing positions due to a difference in the sequence of nozzles to be driven.